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PostPosted: Wed Oct 05, 2011 3:46 am 
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(I am located in the USA)

I have an ENVI energy monitor with a single transmitter and two current transducers (plus a web bridge). The transmitter has 3 sockets total and I am using 2 of them for the 2 current transducers.

My home has 2 independent 200A circuit breaker panels, each being fed by a 240V single-phase pair of wires. I can clamp the current transducers on one or the other of the 240V feeds and monitor the energy usage of just that one panel, but what do I need to monitor both at the same time?

Do I need to buy a second transmitter and 2 more current transducers? (If so, what are the part or model numbers of what I need?) Will my monitor be able to display (and hopefully total) both circuits?

Can I do something "clever" like clamp one of the CT's on a single wire of one feed and the other CT on a single wire of the other feed and then double the displayed Watts? (I am thinking this might actually work if I clamp on the opposing phases.)

Thanks!


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PostPosted: Thu Oct 06, 2011 4:12 pm 
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Location: East Sussex
Are both panels fed from the same electric meter?

If yes, can you move the clamps and transmitter to that location?

Automan.


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PostPosted: Thu Oct 06, 2011 11:21 pm 
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Yes, they are both fed from the same meter, but I do not have access to the wiring at that location (it is inside a locked metal box that only the utility company can access).


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PostPosted: Sat Oct 08, 2011 3:16 am 
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Location: Melbourne, Australia
iamsteve wrote:
My home has 2 independent 200A circuit breaker panels, each being fed by a 240V single-phase pair of wires.
I don't know how accurate a CT would be at 200A*110V=20KVA. Are you expecting it to be fully loaded?
Quote:
I can clamp the current transducers on one or the other of the 240V feeds and monitor the energy usage of just that one panel, but what do I need to monitor both at the same time?
I am uncertain of how you are using the second CT. For one of the CBs you need only one CT clamped to its active wire. Don't clamp the second CT to the neutral wire if that is what you are doing.
Quote:
Can I do something "clever" like clamp one of the CT's on a single wire of one feed and the other CT on a single wire of the other feed and then double the displayed Watts?
Nothing Clever to do. The second CT should be placed on the active wire of the second CB. (assuming they are close enough to to plug into the same transmitter). The enviR will sum the two amounts exactly as if they were two different phases. No need to double.
Quote:
(I am thinking this might actually work if I clamp on the opposing phases.)
You said you have single Phase. Not sure of what you mean by "opposing". I suspect you are referring to the neutral wire.

HTH

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PostPosted: Sat Oct 08, 2011 11:53 am 
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Location: East Sussex
American households typically have a 3 wire single phase and neutral system.

220v between the phase lines and 110v between a phase line and neutral (the 220v needed for larger appliances e.g. the cooker, washer / driers and ac units).

Thus they need two clamps on the two phase lines to measure the house load.

In the UK a property would typically have a single phase and neutral system giving you about 230v (one clamp on the phase line) or a three phase and neutral system with 415v between phase lines and 230v phase line to neutral (3 cc clamps on the phase lines).

Automan.


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PostPosted: Sat Oct 08, 2011 5:30 pm 
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Automan wrote:
Are both panels fed from the same electric meter? If yes, can you move the clamps and transmitter to that location?

They are fed from the same meter but I do not have access to the wiring near the meter because it is contained in a locked metal box that only the electric company has access to.

Automan wrote:
American households typically have a 3 wire single phase and neutral system. 220v between the phase lines and 110v between a phase line and neutral (the 220v needed for larger appliances e.g. the cooker, washer / driers and ac units). Thus they need two clamps on the two phase lines to measure the house load.

Yes -- your description matches my situation. It is just that my house is rather large and therefore I have two circuit panels like this instead of the one that is more typical.

SeekerAfterTruth wrote:
I don't know how accurate a CT would be at 200A*110V=20KVA. Are you expecting it to be fully loaded?

It would be a very rare event to be fully loaded. 200A is just the peak carrying capacity of each panel. Maximum total monthly usage is expected to be about 6000 KWH. Typical would be more like 3500 KWH in a month.

It sounds like what I need to do is go ahead and order a second transmitter, plus two more CT's. Then I would clamp the new CT's on the 'hot' wires feeding the second circuit panel (just like I've done on the first panel). No CT's would be clamped on a neutral wire.

So my only remaining questions relate to whether the ENVI monitor/display would automatically sum the load reported by the two transmitters. The transmitter I have now shows up on the main screen of the ENVI monitor. Would the load measured by the second transmitter appear independently on one of the appliance channels? And then I have to add the two together to know the total load?


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PostPosted: Sun Oct 09, 2011 8:04 pm 
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Location: Melbourne, Australia
Automan wrote:
American households typically have a 3 wire single phase and neutral system.

220v between the phase lines and 110v between a phase line and neutral (the 220v needed for larger appliances e.g. the cooker, washer / driers and ac units).

Thanks for straightening me out. I hadn't seen that arrangement before. I live and learn!.
So, IamSteve, Please ignore what I said before.

For my own understanding I have drawn up drawn up what I think is your arrangement. I Think You have three options, maybe four:
  • As Altman originally said -- move your clamps upstream of the 2 CBs. Depending n how it is wired you may have a single 3-core cable to both CBs or separate cables for each. If the latter you will need to clamp the matching active cores from each cable together. In my case I could not do that because I would need access to the meter Terminals which are sealed against fraud.
  • You cuold buy another transmitter and 2 more clamps. the second transmitter would be tuned to say appliance1 and the ENVIR would not not provide a total.
  • You could use a single clamp for each CB by clamping the two active wires together. However, because of the quirks of your set-up a straight-forward parallel clamp of the wires would not work(labelled BAD ALT in my drawing). Instead you need to reverse the direction of one of the wires as show as GOOD ALT. This may not be feasible because of the thickness of the wires.
  • This is really option 1 but applied downstream of the CBs. The matching wires from each CB need to be clamped together.


One final point. Unless your ENVIR is set up for 110/120V, your power readings will be doubled.

Image

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PostPosted: Mon Oct 10, 2011 6:05 pm 
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SeekerAfterTruth wrote:
You could use a single clamp for each CB by clamping the two active wires together. However, because of the quirks of your set-up a straight-forward parallel clamp of the wires would not work (labelled BAD ALT in my drawing). Instead you need to reverse the direction of one of the wires as show as GOOD ALT. This may not be feasible because of the thickness of the wires. This is really option 1 but applied downstream of the CBs.

Nice drawing! I can't do "Good Alt" because of the thickness/stiffness of the wires, but I don't think it would actually work anyway. I don't think the CT cares which direction the current is flowing so flipping the conductor around shouldn't make any difference. The two signals (and thus their magnetic fields) will still be in opposite phase and would cancel each other out. I believe that would give me the difference in power between the two conductors, not the sum. To get the sum, I'd have to put the clamp around two conductors of the same color (in phase), but those conductors are in two different cabinets.


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PostPosted: Tue Oct 11, 2011 3:33 am 
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Location: Melbourne, Australia
iamsteve wrote:
Nice drawing! I can't do "Good Alt" because of the thickness/stiffness of the wires
I thought that would be the case. In my switchboard there is not enough length to do it. I would need a sparky to rewire that area. (which I would have to do anyway as we are not allowed to open the switchboard in Australia)
Quote:
but I don't think it would actually work anyway. I don't think the CT cares which direction the current is flowing so flipping the conductor around shouldn't make any difference. The two signals (and thus their magnetic fields) will still be in opposite phase and would cancel each other out. I believe that would give me the difference in power between the two conductors, not the sum. To get the sum, I'd have to put the clamp around two conductors of the same color (in phase), but those conductors are in two different cabinets.

Your right that the CT clamp doesn't differentiate the direction of the current . The reason GOOD ALT does work is that the magnetic field created by a current is polarised, so if you have currents in different directions the net magnetic field detected by the CT will be reduced. This is why Current Cost tell us to put the clamp on the active wire not the active/neutral pair (current in neutral is in opposite direction to active so cancels out the reading).

You usage of "opposite phase" is different to the conventional usage. Your two active cables are, conventionally, in-phase (i.e. the voltage rise and fall together) but the current is in opposite directions, so if you do BAD ALT you do get the difference. GOOD ALT, by reversing the current flow of one of the wires through the CT, causes the current to reinforce the other hence you get the addition.

Anyway, enough of self-justification. Are you able to follow ALTMANs recommendation? or will you need to buy additional kit?

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PostPosted: Tue Oct 11, 2011 10:02 am 
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Joined: Sat Apr 16, 2011 1:10 pm
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Location: East Sussex
iamsteve wrote:
Yes, they are both fed from the same meter, but I do not have access to the wiring at that location (it is inside a locked metal box that only the utility company can access).


Perhaps you could ask them again?

All you want to do is fit two clamps around two cables and maybe drill a small whole in the cabinet so the transmitter is outside.

Note: Typical USA electrical cabinets have lots of "knock outs" for cable access. If yes even quicker to do (if outside, pick one on bottom of cabinet).

Automan


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